Since a carbodiimide compound is a rare compound having good reactivity with an acid group such as a carboxyl group, it has been used for crosslinking agents of the like of resins containing mainly acid groups. However, the carbodiimide compound has a characteristic of not only such crosslinking reactivity but also capability of easily introducing various kinds of functional side chains and therefore, in recent years, based on the characteristics, multi-functional polymer compounds have been designed and uses of the compound has been investigated in a variety of fields.
For example, from the viewpoint of application to a pigment dispersion technique, the present inventors promoted development of a method for giving high function of a carbodiimide compound and capability of finely dispersing a hardly dispersible pigment and stably keeping the dispersion state and already proposed the following:    (1) a method for using a carbodiimide group-containing compound as a method for utilizing a covalent bond with a functional group existing in the surface of a pigment (e.g., reference to Patent Document 1);    (2) a method for utilizing acid-base affinity Using a carbodiimide compound as a starting substance, as a method for utilizing the adsorption power of the surface of a pigment (e.g., reference to Patent Document 2); and    (3) a method for utilizing the affinity attributed to analogy of molecular structures (e.g., reference to Patent Document 3).
Such a pigment dispersant which the present inventors propose can deal with high concentration of a pigment and is highly excellent in the dispersion stability and fluidity even in the case of high concentration of a pigment and can give an excellent effect.
Further, the present inventors have found that it is possible to give another different effect to a carbodiimide compound additionally to the basic performance of the pigment dispersibility by introducing a different functional chain other than the above-mentioned functional chain to the carbodiimide compound and have applied for a patent.
This time, the present inventors have made investigations concerning introduction of a functional chain into a carbodiimide compound in order to improve the performance of a dispersant for the dispersion of a pigment, fine resin particles, pigment-resin composite fine particles (colored resin particles), or the like, particularly in a system using a silicone medium as a dispersion medium.
A silicone dispersion medium is used in various fields, in terms of harmless and odorless, high chemical and thermal stability, and a high insulation property and a dispersion medium of a liquid developer is one of the uses. However, so far, no proper material for dispersing a pigment or colored resin particles has been made available and even among the techniques developed and disclosed recently, they are still not efficient.
For example, a technique of treating a pigment-containing toner particles with a silane coupling agent and giving dispersibility is disclosed (e.g., reference to Patent Document 4), however the method is insufficient to cause an efficient effect attributed to a low molecular weight of a silane coupling agent to be used for the treatment.
Further, as a dispersant for dispersing a pigment and a pigment-containing colored resin particles, for example, a technique of using a silicone graft polymer obtained by reaction of a monomer composing a main chain part insoluble in a silicone dispersion medium and a monomer composing a graft parts soluble in a silicone dispersion medium containing a silicone macromer having a polymerizable functional group at the terminal (e.g., reference to Patent Document 5). However, in recent years, in order to obtain higher quality of images, those in which a pigment and colored resin particles are every finely dispersed are required. Since the capability of the above-mentioned dispersants are insufficient, it is required to develop a dispersant having further higher dispersibility.
Patent Document 1: International publication No. 03/076527 pamphlet
Patent Document 2: International publication No. 04/000950 pamphlet
Patent Document 3: International publication No. 04/003085 pamphlet
Patent Document 4: Japanese Kokai Publication No. 2004-093706
Patent Document 5: Japanese Kokai Publication No. 2005-036220